1. Field of the Invention
The present invention relates to an optical pickup device configured to perform at least one operation of optically recording a signal in an optical recording medium and playing a recorded signal, and an objective lens device to be implemented therein, and a driving method of an objective lens.
2. Description of the Related Art
Heretofore, there have been the following objective lenses, as an objective lens implemented in an optical pickup compatible with three formats of BD (Blu-ray Disc™, DVD (Digital Versatile Disc), and CD (Compact Disc) (e.g., see Japanese Unexamined Patent Application Publication No. 2005-302163 (paragraphs [0060] and [0061], and FIG. 7) and Japanese Unexamined Patent Application Publication No. 2005-293770 (paragraph [0038])).
With the optical pickup in Japanese Unexamined Patent Application Publication No. 2005-302163 (paragraphs [0060] and [0061], and FIG. 7), a first objective lens (24) configured to condense a laser beam of a wavelength of 400 through 410 nm into BD (100c), and a second objective lens (25) configured to condense a laser beam of a wavelength of 650 through 780 nm into CD (100b) or DVD (100a) are held in a movable block (12). With this Japanese Unexamined Patent Application Publication No. 2005-302163 (paragraphs [0060] and [0061], and FIG. 7), in order to realize reduction in thickness of a pickup, for example, as shown in FIG. 7, taking into consideration the working distance (WD) of each disc (100), i.e., the distance from each disc to an objective lens, the neutral position of the movable block (12) in the focusing direction is determined. This is because an objective lens compatible with CD and DVD is a two-wavelength compatible objective lens, and in this case, the focal length thereof is generally the same. It is needless to say that compatible objective lenses generally the same focal length. Regardless of the same focal length, the thickness of the cover layer of the disc surface differs between CD and DVD, so it is necessary to consider the neutral position of the working distance as described above. As a result thereof, with regard to each case of CD and DVD, the neutral position of focal stroke (position away from each disc by the working distance) differs. As a result thereof, the focal stroke in total (total stroke) that needs to be secured as optical pickup increases by an amount equivalent to the difference of the neutral position.
The “focal stroke” mentioned here means a range where an objective lens moves by driving of an actuator. With Japanese Unexamined Patent Application Publication No. 2005-302163 (paragraphs [0060] and [0061], and FIG. 7), in order to handle the three formats including BD, the neutral position of an objective lens compatible with BD is designed so as to be positioned in the center between the respective neutral positions of the above-mentioned CD and DVD. Thus, reduction in thickness in the focal direction thereof is realized.
On the other hand, with Japanese Unexamined Patent Application Publication No. 2005-293770 (paragraph [0038]), a three-wavelength compatible objective lens compatible with the above-mentioned three formats is employed.